The advantages of phased array systems are well known in the art of communication and radar systems design. Phased array antennas are constructed with a multiplicity of independently controllable transceivers and antennas. Each transceiver has a transmit path and a receive path and is connected to one or more of the array elements of the array antenna system. The multiple transceiver arrangement of the phased array allows the designer to incorporate into the system a means for independently controlling the signals that are transmitted and received by each transceiver.
By adjusting the phase and amplitude of these signals, a system operator can change the operating characteristics of the system. For example, the width of the electromagnetic beam transmitted from a phased array system can be made broader or narrower by selective phase shifting of the signals transmitted by the individual transceivers. Thus, a phased array system employing variable phase shifters, and a means to control those phase shifters, can have its beamwidth varied without changes to the system hardware. Phased array antenna systems are described in detail in the following references: Radar Handbook, edited by Merrill Skolnik, 2d edition, published by McGraw Hill, Inc. (1990) (see Chapter 7 -9+entitled "Phased Array Radar Antennas" by Theodore Cheston and Joe Frank.); Antenna Theory: Analysis and Design, by Constantine A. Balanis, published by Harper & Row, Inc. (1982) (see Chapter 6 entitled "Arrays: Linear, Planer, and Circular"); Antenna Theory and Design, by Warren Stutzman and Gary Thiele, published by John Wiley & Sons, Inc. (1981) (see Chapter 3 entitled "Arrays", especially section 3.7 entitled "Phased Arrays").
A typical arrangement of transceiver and antenna elements of a phased array antenna system is shown in FIG. 1. In that figure, a phased array system having three transceivers 2 is shown. Each transceiver is connected to one of three radiating elements 3. The transceivers 2 include the following elements: circulators 4, phase shifters 5, transmission amplifiers 6, receiver preamplifiers 7, trimming attenuators 8, and RF switches 8a. Control signals 9 are shown only for the first transceiver. When the system is operating in the transmit mode the switches 8a are set to guide the RF signal down the transmit path of the transceivers 2. The phase shifters 5 are set to the desired transmit phase and the attenuators 8 are set to the desired transmit attenuation, the settings for each transceiver being independent of the settings of the other transceivers. The transmit signal is then amplified by the transmit amplifiers 6 before being radiated from the elements 3. In the receive mode, the circulators 4 and the switches 8a guide the received signal down the receive path of the transceivers 2. The signal is amplified by the receive preamplifiers 7 before being attenuated by trim attenuators 8 and being phase shifted by phase shifters 5. As in the transmit mode, the trim attenuators 8, and the phase shifters 5 may be independently set for each transceiver. It is this ability to independently set the modules that gives rise to many of the advantages of phased array systems.
The advantages realized by the phased array structure find numerous applications in both military and commercial settings. The variable set of operating characteristics that the phased array offers, such as the ability to change beamwidths and gain direction without changing the system hardware or mechanically rotating the aperture, can greatly increase the effectiveness of a military radar. A narrower beamwidth will enable the radar operator to locate a target with greater precision in a particular direction. A broader beamwidth will allow the same operator to find a target more quickly. Ideally the operator would like to begin his search with a broad beamwidth, then upon finding a target, pinpoint the target's position by changing to a narrower beamwidth and a specific direction. A variable beamwidth also offers advantages when employed in a non-military setting.
While phased array systems that realize the advantages of the phased array architecture have been built, there is a desire to make these arrays smaller so that they can be adapted for use in airborne and portable systems.
Traditional phased array radars are bulky complex systems in which azimuth and elevation scanning is accomplished through switching energy and phase by controlling bulky independent phase shifters that are located at each radiating element. The energy is supplied to the antenna by a centralized transmitter--driving it with a low duty cycle, high peak power RF signal which is split and supplied to each phase shifter, each such split and phase-shifted signal being thereafter routed to one or more antenna array elements for transmission. The return signals are sensed by the array elements, operated on by the phase shifters and collected in a centralized receiver for subsequent processing. High Power Systems (e.g. X-Band) using this technology might weigh more than 5 thousand pounds and occupy large structures (greater than 100 ft.sup.3) to house the high power electronics and externally mounted antenna. This combination results in a microwave weight-x-volume product greater than 500,000 lbs.-ft.sup.3.
Active phased arrays reduce the bulk of the above type systems by including miniature solid state RF Transmit/Receive (T/R) modules consisting of amplifier chips for transmit power gain, receiver amplifier chips for receiver gain, and a solid state phase shifter. Low level energy is supplied to the antenna by a high duty cycle, low peak power RF signal which is split and supplied to each T/R element. The T/R modules, while miniaturized, are still complex structures, each consisting of numerous interconnected microwave chips--usually Gallium Arsenide (GaAs) based monolithic microwave integrated circuits (MMICs), deposited on various types of substrates and typically housed in a ceramic or aluminum carrier. This module is typically, 1 inch.times.0.5 inches.times.3 inches and weighs about 2 ounces--depending on the operating microwave frequency of the radar. A ten thousand element antenna (X-Band) using these modules would also include a cooling system, beam forming feeds, and power distribution network. Such a system would typically weigh on the order of 2500 lbs and be about 20 ft.sup.3 in volume. This results in a weight-x-volume product of 50,000 lbs.-ft.sup.3 which is still too large for future stealthy aircraft, surface effect ships, or small tactical ground vehicles.
Two examples of phased arrays which include miniature solid state RF T/R modules are the Westinghouse AN/APQ-164 and the UK's naval phased array (MESAR). In the MESAR system individual GaAs MMIC chips, including a digitally controlled FET phase shifter, are all assembled on an alumina substrate, this technique providing the optimum in cost and yield with the current state of GaAs technology. The Westinghouse system employs 1526 ferrite phase shifters in plug-in module form. The latest developments of this system involve experimentation with complete plug-in GaAs T/R modules.
In overcoming these disadvantages of prior-art systems, the present invention achieves a dramatic reduction in the size and complexity of an active phased array antenna system. This result is accomplished in part through the use of a novel single chip T/R module developed through the use of microwave monolithic integration. Such a single chip T/R module can be realized in a package size of no more than 50 mm.sup.2, thus providing a major reduction in the weight-x-volume product for an array antenna system using such modules. This provides a real breakthrough in the field deployment of advance technology radar systems.